1. Field of the Invention
The present invention relates in general to conduit connections for fluid systems. More particularly, the present invention relates to a composite sleeve seal for a fluid-tight conduit connection between male and female tubular members of an automobile air-conditioning system.
2. Description of the Prior Art
In conventional tubular couplings, standard O-rings are used to seal the connection between tubular members. The O-rings are seated in grooves in a male or female tubular member and are compressed by a complementary female or male tubular member, thereby sealing the connection. The O-ring grooves are generally machined or formed into one of the tubular members as part of a tube end-forming step in the manufacturing process. Performing this step involves extensive process cycle time and total piece costs.
U.S. Pat. No. 4,055,359 to McWethy is an example of the prior art tubular coupling described above. The '359 patent discloses a plurality of O-rings that are compressed in sealed grooves to prevent the coupling from leaking. The O-rings are accommodated by forming spaced circular grooves in the tubular wall of the inner tube.
Alternatively, U.S. Pat. No. 4,690,435 to Manning et al. teaches a hose coupling that is sealed by crimping an outer sleeve over an inner sleeve, compressing and sealing a hose therebetween. The outer sleeve has four axially spaced rings and is crimped at each axially spaced ring creating four annular seals between the hose and the inner sleeve.
Likewise, U.S. Pat. No. 4,407,532 to Patel et al. and U.S. Pat. No. 5,228,721 to Whittle et al. each disclose a crimped connection that enhances sealing by providing ridges or serrations on the outer surface of the inner sleeve, thereby engaging and sealing the hose. For example, the '532 patent discloses a collar having a plurality of barbs on its inner surface and an insert member having a plurality of closely spaced annular ridges for gripping and sealing a hose member. The plurality of barbs on the inner surface of the collar defines a relationship with the plurality of spaced annular ridges on the outer surface of the insert member to provide crimping of the sleeve onto the hose. After crimping the collar about the insert member, with the hose compressed therebetween, the hose is sealingly engaged between the plurality of grooves and the annular ridges in the collar.
The '721 patent discloses a similar arrangement in which the coupling includes a spigot having one or more circumferentially extending ribs for engagement with the inner surface of the pipe member. A shoulder, from which the spigot extends, is coaxially spaced from the spigot with a resilient sleeve therebetween. A crimp ring is slidably mounted over the sleeve for crimpable attachment to the fitting. The circumferentially extending ribs are forced into sealing engagement with the pipe wall and the resilient sleeve ensures the pipe is not damaged. The spigot is either copper or plastic.
U.S. Pat. Nos. 5,044,671 and 5,096,231 to Chisnell et al. disclose a coupling that incorporates an O-ring or resilient sealing member in conjunction with a crimped connection. The '671 reference discloses a hose having an inner liner of thermoplastic material wherein the hose is maintained in compression by a swaged sleeve over a fitting having an O-ring or resilient sealing member located in one of a plurality of grooves into which the thermoplastic liner is cold-formed. The O-ring minimizes the flow of the inner liner at elevated operating temperatures and maintains a seal under varying operating conditions. The '231 reference discloses a resilient sealing member provided on the outer periphery of the fitting to sealingly engage a hose member and provide a seal therebetween.
Each of the above references provides a sealing arrangement that adequately seals a coupling. However, all of the couplings described above require extensive tube end-forming operations to create the grooves that contain the resilient sealing members, or the ridges and circumferentially extending ribs that sealingly engage a hose member.
Furthermore, O-rings are known to be relatively unreliable and subject to failure over time. O-rings provide a good seal when they are at 6% compression. Due to tolerance stack up of the machined groove, the O-ring, and the tubular members, the range of O-ring compression is between 2% and 15%. If the compression is less than 6%, leaks will occur. Alternatively, if the compression is over 15%, several other problems will occur, including: 1) the coupling becomes extremely difficult to assemble over the O-ring; 2) the O-rings undergo considerable deformation during the coupling process; 3) the life of the O-ring becomes substantially reduced when subjected to high heat; and 4) the O-rings easily become nicked or otherwise damaged resulting in premature failure and poor sealing ability, thereby causing leaks. Thus, there is a need for a more reliable and longer lasting seal for tubular couplings.
Conventional tube end-forming operations are also relatively difficult processes to control. The tube wall is thickened by a punching operation that compresses a length of tube. The punching operation is not very repeatable, as it is very material dependent, and results in a large range of dimensional tolerances for the finished product. After the tube wall is thickened the O-ring grooves are cut into the thickened end of the tube. During the cutting operation the tube is held a certain distance from the thickened end, which permits flexing in the tube, resulting in uneven cuts. Also, the particles or chips left behind in an uneven cut can cut the O-ring and lead to premature failure thereof. In sum, poor surface finish and chips resulting from conventional tube end-forming contribute to the O-ring sealing surfaces being unacceptable for proper sealing.
Another problem with conventional tube end-forming processes is side loading that can occur when the tubular connection is torqued. When the connection is torqued, the O-ring can become pinched in one area and decompressed in another area. The decompressed area of the O-ring becomes a leak path. Additionally, under side load conditions the O-ring is assured of failing when subjected to the harsh pressure, temperature, and vibration conditions of a vehicular air-conditioning system.
One attempt at eliminating such end-forming operations was disclosed in U.S. Pat. No. 4,781,400 to Cunningham. The Cunningham reference teaches a quick connect tube coupling using a two-piece tubular seal member placed over a male member for providing the effect of two O-rings, without requiring any special end-forming operation. Cunningham discloses the tubular seal member including a metal tubular member having a rubber material molded onto one end thereof. The tubular seal member is sandwiched between a male tubular member and a female tubular member. The rubber material includes inwardly extending beads and an axial portion for sealing axially against the female tubular member and for sealing radially against the male tubular member.
While the Cunningham reference enables elimination of end-forming requirements for tubular connections, it has a few drawbacks. For example, the rubber material is not positively interlocked with the underlying metal tubular member and therefore may more easily become separated therefrom. Additionally, the rubber material seals only axially, and radially inwardly, which is quite unlike how traditional O-rings seal. Traditional O-rings seal both radially inwardly and outwardly, and thereby better center the male tubular fitting within the female fitting. Accordingly, with Cunningham there is no continuity of the rubber sealing surface from a radial surface on the male tubular fitting to a radial surface in the female tubular fitting.
Another attempt at eliminating end-forming operations was disclosed in French Patent 2,740,526 to Baron. The Baron reference teaches use of a composite gasket of alternating collars and rings to be circumferentially disposed about the end of a tube within a tubular connection. The Baron reference discloses rigid collars in the shape of cylindrical sleeves that alternate coaxially with elastomer rings to define the gasket. The collars are integrally fixed to the rings by a gluing, casting, or vulcanizing process.
While the Baron reference represents another approach to eliminating end-forming operations, it also has several drawbacks. First, each alternating collar and ring must be individually manufactured, resulting in an abundance of individual parts to be made and handled. Second, each individual collar or ring must be assembled to one another, representing more manufacturing steps and cost. Third, each alternating collar and ring must be fused together, thus resulting in still more manufacturing steps. Fourth, due to the harsh environment in which such gaskets are used, a fused connection between the collars and rings may separate. Consequently, the manufacture of the gasket is relatively time consuming and expensive, while performance of such a fused thermoplastic in a demanding environment is not well established.
Prior art tube end-forming operations are time consuming and therefore expensive. Generally, what is needed is a simplified means for sealing a coupling that does not require separate O-rings mounted in machined or formed grooves. The extensive tube end-forming operations, such as machining grooves, or forming circumferentially extending ribs, need to be eliminated to reduce cost. Accordingly, what is needed is a fluid-tight conduit connection that requires neither extensive tube nor seal manufacturing operations and will enhance the sealing capability of a tubular coupling.